I’m sorry for your loss anon. I have never owned a debarked dog so please take my advice with a grain of salt! Hopefully our followers can give you some hands-on experience.
First off, it’s going to take some time for this new dog to adjust. Going from an older or ill household (ie probably a very quiet household) to a household with multiple people and two resident dogs (ie probably a fairly active or busy household) is a big change for a dog! Be patient and consistent and fair and give the dog a few weeks to adjust.
Once the dog adjusts and you get to know him, you’ll be able to read his body language a bit better. Obviously for now he’s going to be pretty uncomfortable (see last point) so just give him time. Since he can’t bark at your resident dogs to tell them to leave him alone, offer him plenty of alone time and try to avoid any situations that might cause discomfort (feed him alone, offer him his own water bowls and toys).
Hopefully as he settles in, you’ll be able to read him better. Some dogs aren’t very vocal by nature so hopefully he will be able to communicate anyway. Good luck!